The Q&A Archives: Flower Color on Hydrangea

Question: Does the hydrangea require acid soil in order to produce blue blossoms?

Answer: Yes! The flower color is determined by the availability of aluminum in the soil. In alkaline soils, the aluminum in the soil is in a form that is unavailable to the plants. In soils with a pH of 7 to 7.5, expect pink flowers. In acid soils, the aluminum is in a form that the roots can take up, so in soils with a pH of 4.5 to 5.5, expect blue flowers. In between, in soils with a pH between 5.5 and 7, the color will range from bluish to mauve to pinkish. (This of course refers to colored varieties of Hydrangea macrophylla. There are also white cultivars.)

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